The present invention generally relates to advanced medical endoluminal devices and methods of minimally invasive treatment of blockages of the blood vessels and other tubular organs. More particularly, the present invention relates to apparatus for delivering, repositioning and/or retrieving self-expanding stents for internal reinforcing of diseased tubular structure and/or for local delivery of pharmacological or radioactive agents having a beneficial advantage of reduction of re-stenosis.
Reference is made to a related application entitled Methods for Delivery Repositioning and/or Retrieving Self-Expanding Stents filed concurrently with this application.
A stent is a generally longitudinal cylindrical device formed of biocompatible material, such as a metal or plastic, which is used in the treatment of stenosis, strictures, or aneurysms in body blood vessels and other tubular body structures, such as the esophagus, bile ducts, urinary tract, intestines or tracheo-bronchial tree. References hereafter to xe2x80x9cblood vesselsxe2x80x9d and xe2x80x9cvesselsxe2x80x9d will be understood to refer to all such tubular body structures. A stent is held in a reduced diameter state during its passage through a low profile catheter until delivered to the desired location in the blood vessel, whereupon the stent radially expands to an expanded diameter state in the larger diameter vessel to hold the vessel open. As discussed below, radial expansion of the stent may be accomplished by an inflatable balloon attached to a catheter, or the stent may be of the self-expanding type that will radially expand once deployed from the end portion of a delivery catheter.
Non-diseased vessels that are stented have a tendency to develop more aggressive intimal hyperplasia than diseased vessels. Intimal hyperplasia is part of the endothelialization process by which the stent becomes incorporated into the vessel wall as a result of the vessel""s reaction to a foreign body, and is characterized by deposition of cell layers covering the stent. It eventually results in formation of a neointima, which coats the stent and buries it completely in the vessel wall.
Endothelialization generally improves patency rates and the more complete the apposition of the stent to the vessel wall, the more uniform and optimal is the degree of endothelialization. Of course, a fundamental concern is that the stent be deployed in the correct desired location in the vessel as precisely as possible in the first place. This is important when delivering radiation or medication to a particular location using the stent.
Therefore, firstly, it is important that a stent be deployed in the correct desired position in the blood vessel and, secondly that the stent be as completely apposed to the vessel wall as possible.
Stents fall into one of two categories based on their mechanism of deployment and radial expansion, namely, balloon-expandable stents and self-expanding stents.
Balloon-expandable stents (BES) are mounted in their reduced diameter state on nylon or polyethylene balloons, usually by manual crimping, while others are available pre-mounted. One example of a BE is shown in U.S. Pat. No. 4,733,665 to Palmaz. BES rely solely on balloon dilation to attain the desired expanded configuration or state. This enables BES to be deployed in a relatively controlled gradual manner. BES in general have more strength than self-expanding stents and initially resist deformation as well as recoil. BES behave elastically but eventually yield and become irreversibly, i.e. plastically, deformed under external force. Most BES are less flexible than self-expanding stents and are therefore less capable of being delivered through tortuous vessels and, when a BES is deployed in a tortuous vessel, it often straightens the vessel, forcing the vessel to conform to the shape of the stent rather than vice versa. This generally results in portions of the stent not being completely apposed to the vessel wall which in turn affects endothelialization and overall patency rate.
On the other hand, BES can generally be deployed in a relatively precise manner at the correct desired location in the vessel since they can be deployed in a controlled gradual manner by gradually controlling the inflation of the balloon. This ability to gradually control the expansion of the stent, along with the fact that BES rarely change their position on the balloon during inflation, enable fine adjustments to be made by the operator in the position of the stent within the vessel prior to stent deployment.
Self-expanding stents (SES) are formed of braided stainless steel wire or shape-memory alloy such as nitinol and are generally delivered to desired locations in the body in a reduced diameter state in a low profile catheter while covered by an outer sheath which partially insulates the SES from body temperature and mechanically restrains them.
Nitinol is an alloy comprised of approximately 50% nickel and 50% titanium. Nitinol has properties of superelasticity and shape memory. Superelasticity refers to the enhanced ability of material to be deformed without irreversible change in shape. Shape memory is the ability of a material to regain its shape after deformation at a lower temperature. These physical properties of nitinol allow complex device configurations and high expansion ratios enabling percutaneous delivery through low profile access systems.
Superelasticity and shape memory are based on nitinol""s ability to exist in two distinctly different, reversible crystal phases in its solid state at clinically useful temperatures. The alignment of crystals at the higher temperature is called the austenite (A) phase; the alignment of crystals at the lower temperature is called the martensite (M) phase. In between is a temperature interval of gradual transition between the A and M phases.
Under external force, the shape of a nitinol device can be greatly deformed without irreversible damage. Depending on the temperature at which this external force is applied, superelastic or shape memory effects prevail. In close vicinity to or above the temperature defining transition into the full A state, superelasticity results: as soon as the deforming force is released, the device immediately assumes it original shape. When nitinol is deformed at or below the lower temperature of the complete M transition, the shape memory effect can be exploited. The device retains its deformed shape even after the external force is removed as long as the temperature of the environment stays below the temperature of transition into A phase. Only during heating does the device resume its original shape.
While the shape memory effect is essentially a one-way type phenomena in which shape recovery occurs only upon heating the alloy to a temperature defining transition to the full A phase, by subjecting the alloy itself to a biasing force, i.e. an internal stress formed by dislocations introduced by plastic deformation in the alloy, a two-way shape memory can be imparted to the alloy so that cooling the alloy will induce a shape change.
One type of self-expanding stent is constructed of wire formed of a shape-memory alloy, such as nitinol, having a transition temperature of about body temperature, i.e. 37xc2x0 C. For example, reference is made to U.S. Pat. No. 5,746,765 to Kleshinski et al. The one-way transition temperature is the temperature of transformation of a nitinol device from its collapsed state into a fully expanded configuration. The stent is preloaded on a low profile catheter by crimping the stent at room temperature (at which it can be plastically deformed) onto the catheter. An outer sheath covers the crimped stent and at least partially thermally insulates the stent as it is delivered to the desired location. Upon reaching the desired location, the sheath is withdrawn and the stent is exposed to body temperature whereupon it is naturally warmed to body temperature and expands to its expanded diameter state in supporting contact with the vessel wall. In a fully expanded state within the human body, the stent is capable of exerting considerable radial force on the surrounding structures, which allows mechanical opening of the vessel lumen and maintaining its long-term patentcy for free passage of flow.
If an alloy is used for which shape recovery occurs above body temperature, the SES must be heated after release into the body. If shape recovery occurs below body temperature, the device may be cooled during the delivery to prevent expansion inside the delivery catheter. If shape recovery occurs at body temperature, no heating or cooling is necessary during the delivery and deployment, provided delivery is relatively speedy. If, however, a tortuous iliac anatomy or other interference delays prompt deployment of a nitinol stent with these characteristics, premature warming to body temperature could cause expansion in the delivery sheath, increase friction, and interfere with delivery. In this instance, flushing with a cool solution has been suggested.
SES do not require any special preparation prior to deployment. SES behave elastically throughout their lifetime, and do not become irreversibly deformed. When deployed, the nominal diameter is purposely selected to be greater that the diameter of the vessel. Therefore, once deployed, an SES exerts continuous outward force on the vessel as it tries to expand to its original dimensions. The ability of an SES to continuously exert an outward force on the vessel coupled with the greater flexibility of SES, generally results in optimal wall apposition, thereby optimizing endothelialization and improving patency rates. Nitinol self-expanding stents have been designed having good radial and hoop strength.
However, while SES are preferable relative to BES in many applications with respect to achieving optimized endothelialization and increased patency rates, currently available arrangements for delivering and deploying SES are not entirely satisfactory. It has generally not been possible to deploy SES in the correct desired location in a vessel as precisely as in the case of BES with currently available delivery arrangements for the reason that the temperature of the SES rapidly increases to body temperature upon withdrawal of the outer sheath and therefore the stent quickly expands into engagement with the vessel wall. Consequently, there is not always enough time to finely adjust the position of the SES as it quickly expands, and it is not uncommon for the distal end of an SES, which is exposed to body temperature first, and which therefore expands before the rest of the SES, to engage and become attached to the vessel wall in the wrong position and in turn inhibit or prevent further adjustments in the position of the SES in the vessel.
Another drawback in conventional arrangements for delivering and deploying SES, as compared to BES, is that during deployment while BES are advantageously pressed against the vessel wall with a relatively large outward force by the dilating balloon in the manner of an angioplasty to insure attachment of the BES to the vessel wall, SES must rely solely on the outward force exerted by the expanding SES to provide initial attachment. It is common to supplement the SES placement with a subsequent balloon angioplasty, which requires exchange of the stent delivery system after completion of stent deployment for a balloon catheter.
Still another drawback in conventional arrangements for delivering and deploying SES is the possibility that when delivery is protracted, the SES is exposed to body temperature inside the delivery system. The deployment process can then become more difficultxe2x80x94the device may open abruptly after being freed from the system and may xe2x80x9cjumpxe2x80x9d beyond the target as the SE expands during deployment. BES cannot be repositioned or retrieved after deployment and while arrangements have been proposed for enabling the repositioning and/or retrieval of SES formed of two-way shape memory material, no practical workable arrangement has been developed.
A malpositioned stent often requires an additional stent placement to correct the mistake and achieve the desired results. The stents will remain in the vessel for the entire life of the patient. In a high percentage of patients, the stent will become the site of recurrent stenosis due to an aggressive neointimal proliferation. These patients require repeated interventions, which often include balloon angioplasty and/or additional stent placement.
The most striking illustration of these problems is seen in cardiac patients. Stents and balloon angioplasty transformed the care of patients with heart disease. Each year, about 700,000 patients in the U.S. undergo angioplasty, in which a balloon is used to clear an obstruction in a coronary artery and a stent is deployed to keep it open. Yet a disturbingly high 15% to 20% of the procedures fail within six months, due to the aggressive neointimal proliferation. These patients will often undergo further major treatments, which might be repeated several times.
The need to be able to reposition and/or retrieve stents from a vessel also arises from the fact that heart researchers and stent manufacturers are developing a new generation of stents that not only prop open the vessel, but which deliver drugs to the site of the blockage in an effort to minimize or eliminate neointimal proliferation and keep the vessel open for long periods of time. Studies have shown that stents coated with a drug called rapamycin, essentially eliminates re-stenosis. Other medications, such as nitric oxide and paclitaxel or similar compounds, also have a potential to prevent proliferation of scar tissue by killing such cells. One concern is whether the drugs might work too well, inhibiting not only re-stenosis, but also the necessary growth of the thin layer of neointima. As previously described, this thin layer of cells, which grows over the stent, smoothes its surface (similar to a layer of Teflon), so blood cells can flow over it without damaging themselves. A damaged blood cell initiates a chemical cascade, which results in clot formation. Therefore an exposed bare metallic stent carries a risk of inducing thrombus formation within it.
The potential of radioactive stents to prevent re-stenosis is an additional area of active research, since local radiation has been shown to inhibit the growth of neointima and halt the progression of atherosclerotic disease.
One can therefore appreciate the benefit of being able to retrieve a stent used for local drug delivery or radiation treatment, after it has achieved its desired effect. This would eliminate potential risk of thrombus formation at the site of the exposed bare stent.
In summary, ideally an optimal stent and associated delivery system should possess and combine all the positive traits mentioned so far in each of the stent categories. The stent should be pre-loaded on the delivery apparatus and should not require special preparation. It should be flexible to enhance apposition to the vessel wall. It should provide a controlled gradual deployment without stent migration to ensure deployment of the stent in the correct location. Lastly, in case of a malpositioned stent, or stent which is deployed for the purpose of its temporary effect, such as for local drug delivery, the system should have the option of enabling repositioning and/or retrieval of the stent.
SES can be preloaded on the delivery apparatus, do not require special preparation and are flexible. However, to date, no satisfactory method or apparatus is available for obtaining a controlled gradual deployment of an SES without stent migration, or for repositioning and/or retrieving a SES. While arrangements have been suggested in the prior art for delivering SES to a correct location in a precise manner and for repositioning and retrieving SES formed of two-way shape memory material, these prior art arrangements all have drawbacks and have not been adopted in practice.
An arrangement for delivering, repositioning and/or retrieving an SES formed of a two-way shape memory alloy capable of expansion or collapsing in the radial direction in accordance with changes in temperature is disclosed in U.S. Pat. No. 5,037,427 to Harada et al. According to Harada et al., a stent is made of nitinol alloy trained to have two-way shape memory. The stent is in an expanded diameter state at about body temperature and in a reduced diameter state at a temperature below body temperature. In delivering the stent, the stent is mounted in the reduced diameter state at the distal end of a catheter over a portion of the catheter having a number of side ports. Cooling water supplied through the catheter flows out from the side hole and is brought into contact with the stent during delivery to maintain the stent below body temperature and therefore in the reduced diameter state. When the SES is positioned at the desired location, the supply of the cooling water is stopped and the stent is warmed by the heat of the body and expands into supporting engagement with the wall of the vessel. The catheter is then withdrawn. In retrieving an already-positioned SES using this system, the distal end portion of the catheter is inserted into the expanded stent lumen and a cooling fluid is introduced into the catheter and discharged through the side ports at the distal end region into the vessel whereupon the stent is cooled and purportedly collapses onto the distal end portion of the catheter. The stent is retrieved by withdrawing the catheter. The patent suggests that the position of the stent can also be changed using this technique.
U.S. Pat. No. 5,746,765 to Kleshinski, Simon, and Rabkin also discloses a stent made from an alloy with two-way shape memory, which expands inside the vessel due to natural heating to body temperature. The stent is covered with an elastic sleeve. When the metal frame is softened by decreased temperature, the sleeve overcomes its radial force and promotes its further contraction for easier retrieval.
However, in both the arrangements disclosed in Harada et al. and Kleshinski et al., a substantial amount of very cold solution must be infused into the vessel in order to reduce the local temperature of the environment surrounding the stent. Cold temperature around the stent must be maintained for some time until the stent is delivered or recovered for retrieval or repositioning. This technique appears to be clinically impractical and not safe due to high risk of potential tissue and blood cell damage.
U.S. Pat. No. 6,077,298 to Tu et al. discloses a retractable stent made from a one-way shape-memory alloy, such as nitinol, that can be deployed into the body by means of dilation with a balloon catheter. For the stent retrieval, a radio frequency current within the range of 50 to 2,000 kHz must be applied directly to the stent to provide partial collapse of the stent after it is heated to a temperature above 43xc2x0 C. to 90xc2x0 C. However, if the transition temperature of the stent material is in the range of 43xc2x0 C.xe2x88x9290xc2x0 C., the radial force of the device will be greatly reduced at the body temperature of 37xc2x0 C., and may not be sufficient for therapeutic effect. Heating of the stent to almost a boiling temperature can cause irreversible damage to vascular wall and blood coagulation.
U.S. Pat. No. 5,961,547 to Razavi, U.S. Pat. No. 5,716,410 to Wang et al., U.S. Pat. No. 5,449,372 to Schwaltz et al. and U.S. Pat. No. 5,411,549 to Peters disclose temporary or retractable stents in the shape of a spiral coil or a double helix. Although these stents are made of different materials, such as metal or plastic, and have differences in the techniques of their deployment (heat-activated, self-expanding or balloon expandable), as well as methods of their retrieval (mechanical straightening vs. softening by increasing temperature vs. latch retraction), all of them have one common feature. The stents are connected with a wire extending outside the patient at all times and when they have to be removed, they are simply retracted back into the catheter with or without prior softening of the material. For this reason these stents cannot be left in the human body for more than a couple of days. The connecting wire can traverse the entire body if the stent is placed in the coronary or carotid artery from the femoral approach, increasing risk of thrombus formation around the wire and distal embolization, thrombosis of the femoral artery and infection of the inquinal region.
U.S. Pat. No. 5,941,895 to Myler et al. discloses a removable cardiovascular stent with engagement hooks extending perpendicular to the axis of the stent into the vessel lumen. The stent retrieval technique requires introduction of an extraction catheter, which is adapted to grasp the engagement hooks of the stent with subsequent stent elongation in axial direction and reduction of its cross-sectional diameter. However, the stent with inwardly extending engagement members will likely require a larger delivery system than regular tubular devices. Any manipulation of the catheters and guidewires in the stented area may potentially accidentally engage the hooks of the stent with its subsequent dislodgment and damage of, the vessel. The hooks extending into the vessel lumen will cause turbulence of blood flow around them, leading to activation of the coagulation system and thrombus formation.
U.S. Pat. No. 5,833,707 to McIntyre et al. discloses a stent formed from a thin sheet of metal that has been wound around itself into a general cylindrical tight roll and expands inside the body by heating to body temperature. This stent is designed for predominant use in the human urethra and is not suitable for cardiovascular applications due to very large metal surface that could be thrombogenic and increased size of the delivery system. The stent can be removed from the body with the help of a cannula or pincer grips for grasping the edge of the stent. By rotating the pinched stent, the pincer or cannula cause the stent to telescopically coil into smaller diameter, which can then be retrieved from the urethra. This technique could be too traumatic for cardiovascular applications. The recovery apparatus will likely have a large profile, making this method not practical or feasible for percutaneous use in blood vessels or other tubular organs.
U.S. Pat. No. 5,562,641 to Flomenblit et al. discloses a spiral or cylindrical stent made from alloy with two-way shape memory capabilities. The stent expands inside the body by heating to the temperature of 50xc2x0 C. to 80xc2x0 C. with an electric current, injection of hot fluid, external radio frequency irradiation or use of radio frequency antenna inside the catheter. The stent can be removed from the body after cooling to a temperature, ranging from xe2x88x9210xc2x0 C. to +20xc2x0 C., at which the stent partially collapses in diameter and can be grasped with a catheter for retrieval. As discussed above, heating of the stent to a temperature over 80xc2x0 C. could be unsafe, especially with intravascular injection of hot fluid. Use of external radio frequency irradiation will cause heating not only of the stent, but all tissues from the skin surface to the stented vessel deep inside the body and beyond. Cooling the stent to below the freezing temperature by injection of a very cold fluid into a blood circulation for removal is also impractical and not feasible in a real clinical setting.
Accordingly, it is an object of the present invention to provide new and improved apparatus for delivering stents to desired locations in blood vessels and other tubular body structures.
Another object of the present invention is to provide new and improved apparatus for delivering self-expanding stents to desired locations in body vessels by which the stent can be deployed in a controlled gradual manner to thereby enhance the accuracy of positioning.
Still another object of the present invention is to provide new and improved apparatus for delivering self-expanding stents to desired locations in body vessels by which the stent can be deployed in a controlled gradual manner safely without infusing a cooling liquid into the vessel or otherwise affecting general body temperature or causing systemic affects.
Yet another object of the present invention is to provide new and improved apparatus for delivering self-expanding stents to desired locations in body vessels which eliminate the possibility of migration of the stent during deployment.
A further object of the present invention is to provide new and improved apparatus for repositioning and/or retrieving self-expanding stents in and from a body vessel without infusing a cooling or heating liquid into the vessel or otherwise affecting general body temperature or causing systemic affects.
A still further object of the present invention is to provide new and improved apparatus for repositioning and/or retrieving self-expanding stents which eliminates the possibility of migration of the stent during repositioning.
A still further object of the present invention is to provide new and improved apparatus for providing supplemental balloon angioplasty after stent deployment with the same system, eliminating the need for exchanging catheters.
Briefly, in accordance with one aspect of the present invention, these and other objects are attained by providing an arrangement for delivering a self-expanding stent formed of a shape memory alloy to a desired location in a body vessel by placing the stent in a collapsed condition in contact, or in other local heat transfer relationship, with a thermal transfer device coupled to a catheter assembly, and delivering the stent in its collapsed condition to the region of the desired location in the body vessel while in contact or other local heat transfer relationship with the thermal transfer device. According to the invention, the temperature of the thermal transfer device can be controlled in a safe and non-invasive matter so that the expansion of the stent can be controlled (thereby enabling the precise positioning of the stent) by suitably varying the temperature of the thermal transfer element, and therefore the stent, during delivery and/or deployment.
For example, in the case where the stent is made of a shape memory alloy having a transition temperature such that the stent from which it is formed is in its expanded diameter state at or slightly below body temperature (37xc2x0 C.), the temperature of the thermal transfer device is maintained below body temperature during delivery of the stent and at the beginning of deployment to allow precise positioning, while in the case where the stent is made of a shape memory alloy having a transition temperature such that the stent obtains its expanded diameter state at a temperature greater than body temperature, the temperature of the thermal transfer element is increased to the higher temperature after the stent in its collapsed state has been precisely positioned at the desired location whereupon the stent expands to its expanded diameter state.
The thermal transfer device is constructed such that the temperature of the stent can be controlled quickly, precisely and non-invasively. Specifically, the temperature of the stent can be changed quickly since the stent is in local heat transfer relationship with the thermal transfer device. For present purposes, xe2x80x9clocal heat transfer relationshipxe2x80x9d means either the stent contacts the thermal device or the stent and thermal transfer device are sufficiently close, so that heat is transferred between the stent and the thermal transfer device without materially affecting the temperature of the surrounding tissue. The stent""s temperature can be controlled relatively precisely since the temperature of the stent, which has a low mass, will essentially correspond to the temperature of the thermal transfer device, which has a much higher mass. Moreover, no liquid or gas will be infused into the vessel during the entire procedure, such as in the case of Harada et al U.S. Pat. No. 5,037,427.
In preferred embodiments of the invention, the thermal transfer device comprises an arrangement itself capable of controlled radial expansion to about the diameter of a stent in its expanded diameter state, and contraction to a collapsed state. This feature, in some of its embodiments, is not only advantageous with respect to the initial delivery of a self-expanding stent with an option of performing a balloon angioplasty at the same time, but, additionally, makes the arrangement particularly adapted for repositioning and/or retrieving stents formed of two-way shape memory alloys that have already been deployed in a vessel, such as in the repositioning of a misplaced stent, removal of a stent placed for temporary indications, or the removal of a stent that has completed the delivery of mediation or radiation to a particular area. Specifically, for removal and/or repositioning of the stent, the thermal transfer device is structured and arranged to be initially positioned in the lumen of the already deployed stent in a collapsed condition, out of contact or other local heat transfer relationship with the deployed stent, and then expanded into contact, or other local heat transfer relationship with the stent. The temperature of the heat transfer device is adjusted so that the temperature of the deployed stent is reduced to that at which the stent obtains a relaxed, flexible state whereupon it separates from the vessel wall. The stent can then be drawn into the catheter assembly and either removed from the body or repositioned using the initial delivery process described above.
In one embodiment in which the thermal transfer device comprises an inflatable and expandable balloon member, the initial delivery of a stent formed of a shape memory alloy can be assisted in the manner of angioplasty by inflating the balloon to forcibly urge the stent against the vessel walls.
In accordance with another aspect of the invention, the catheter assembly includes a capturing device for releasably coupling the stent to the catheter assembly during deployment, as well as for grasping an already-deployed stent for purposes of retrieval and/or repositioning. The capturing device prevents the stent from being carried away by the bloodstream or from migrating on the catheter, and is also structured and arranged to assist in drawing the stent in its flexible and pliable condition into the catheter assembly for repositioning and retrieval.
In a preferred embodiment, the thermal transfer device comprises a balloon member connected to a catheter assembly defining a contained chamber having an outer wall, at least a part of which constitutes a thermal transfer material. The arrangement further includes apparatus for circulating a thermal transfer fluid from the proximal end region of the catheter assembly into the interior of the chamber and for providing an outflow of the thermal transfer fluid from the interior of the closed chamber to the proximal end region of the catheter assembly. As used herein, the term xe2x80x9cfluidxe2x80x9d refers to either a liquid or a gas. The temperature of the circulating thermal transfer fluid is controlled either by heating or cooling means situated at the proximal end of the catheter assembly outside of the body, or by heating means situated within the chamber of the thermal transfer device, such as optic fibers for transmitting a laser beam to heat the fluid circulating within the thermal transfer device, an internal ultrasound probe situated within the thermal transfer device, or a spiral resistance heating wire which will be heated by induction of an electric current by applying the power source or magnetic field from an external source. Alternatively, the surface of the balloon can be heated for direct heat transfer to the stent. For example, resistance heating wires may be situated on the outer surface of an expandable balloon, as can a spiral surface wire which can be heated by induction through the application of a power source or magnetic field from an external source, or externally situated optic fibers for transmitting a laser beam along and around the surface of the balloon. The stent is in contact with the heat transfer surface during delivery and depending on the transition temperature of the alloy from which the stent is made, the stent is either cooled, heated, or left at ambient temperature through contact or other local heat transfer relationship during delivery. In capturing an already deployed stent, the balloon in its collapsed condition is situated in the lumen of the already deployed stent, and then expanded into contact with the stent. Cooling liquid is circulated through the balloon which cools the stent causing it to separate from the vessel wall and to become flexible and pliable so that it can be drawn into the catheter assembly.
In another preferred embodiment, the thermal transfer device comprises an expandable frame formed from a plurality of conductive resistance wires. The frame can be expanded by suitable adjustment of the catheter assembly to bow the resistance wires radially outwardly into contact with the stent. The wires are heated by connection to an external source of electricity and are in direct contact heat transfer relationship with the stent.